Sildenafil is a widely recognized medication that has transformed the treatment of erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). Marketed under brand names like Viagra and Revatio, Sildenafil has provided relief and improved the quality of life for millions of people around the world. Whether you’re considering Sildenafil for ED or PAH, this guide will cover everything you need to know, from how it works to potential side effects and interactions. Understanding the nuances of this medication is essential for both patients and healthcare providers.

What is Sildenafil?

Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor that works by relaxing the muscles of blood vessels, thus increasing blood flow to certain areas of the body. This increased blood flow is crucial for treating conditions like ED and PAH.

Viagra: Sildenafil is most famous for treating erectile dysfunction under the brand name Viagra. It helps men achieve and maintain an erection when sexually stimulated by increasing blood flow to the penis.

Revatio: Another formulation of Sildenafil, known as Revatio, is used to treat pulmonary arterial hypertension, a condition characterized by high blood pressure in the lungs’ arteries. By relaxing blood vessels in the lungs, Revatio reduces the blood pressure in these vessels, improving exercise capacity and slowing down the progression of the disease.

Important Note: Do not take Viagra if you are already taking Revatio, as this could lead to an overdose of Sildenafil.

Uses of Sildenafil

Erectile Dysfunction (ED): Sildenafil, commonly known by its brand name Viagra, is primarily used to treat erectile dysfunction (ED) in men. ED is a condition where a man experiences difficulty achieving or maintaining an erection during sexual activity. Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. It works by blocking the action of an enzyme known as cGMP-specific phosphodiesterase type-5 (PDE-5), which helps maintain an erection by increasing blood flow to the penis when sexually stimulated

Pulmonary Arterial Hypertension (PAH): Sildenafil is also used to treat pulmonary arterial hypertension (PAH) in both men and women. PAH is a type of high blood pressure that occurs between the heart and the lungs. When hypertension affects the lungs, the heart must work harder to pump blood through the lungs. Sildenafil acts on the PDE5 enzyme in the lungs, relaxing blood vessels and increasing blood supply. This reduces the workload on the heart and improves exercise capacity

How Does Sildenafil Work?

Sildenafil works by inhibiting the enzyme phosphodiesterase type 5 (PDE5). By blocking this enzyme, Sildenafil prevents the breakdown of cyclic guanosine monophosphate (cGMP), a molecule that relaxes smooth muscle cells and dilates blood vessels. This action is critical for increasing blood flow to the penis in men with ED and for reducing pulmonary blood pressure in patients with PAH.

ED Treatment:

• In men with ED, the PDE5 enzyme breaks down cGMP too quickly, preventing sufficient blood flow to the penis during sexual stimulation.
• Sildenafil inhibits PDE5, allowing cGMP levels to rise and promoting sustained blood flow to the penis. This facilitates an erection.

PAH Treatment:

• In PAH, the blood vessels in the lungs constrict, leading to increased pressure in the pulmonary arteries.
• Sildenafil also acts on PDE5 in the lung blood vessels, causing vasodilation and reducing pulmonary artery pressure.
• Improved blood flow helps alleviate symptoms and enhances exercise capacity in PAH patients.

Warnings and Precautions

Before you start taking Sildenafil, it’s crucial to be aware of several warnings and precautions:

Nitrate Interactions: Do not take Sildenafil if you are also using nitrate medications, which are often prescribed for chest pain or heart problems. This includes drugs like nitroglycerin, isosorbide dinitrate, and isosorbide mononitrate. Additionally, recreational drugs like “poppers” (amyl nitrate or nitrite) should be avoided. Combining Sildenafil with nitrates can lead to a severe and potentially life-threatening drop in blood pressure.

Other Medications: Certain medications can cause dangerous interactions with Sildenafil. For instance, if you are taking Riociguat (Adempas) for PAH, you should avoid Sildenafil. Always inform your healthcare provider about all the medications you are taking to prevent harmful interactions.

Priapism Warning: Sildenafil can cause priapism, a condition where an erection lasts longer than four hours. This is a medical emergency that can cause permanent damage to the penis if not treated promptly.

Sudden Vision Loss: Although rare, some people taking Sildenafil have experienced a sudden loss of vision. This condition, known as non-arteritic anterior ischemic optic neuropathy (NAION), has occurred primarily in people with pre-existing heart conditions, such as diabetes, high blood pressure, high cholesterol, or certain eye problems, and in those who smoke or are over 50 years old.

Before Taking Sildenafil

Allergies: Do not use Sildenafil if you are allergic to it or any of its ingredients. Allergic reactions can range from mild to severe, and it is essential to be aware of any potential allergies before starting treatment.

Medical History: Your healthcare provider needs to know your complete medical history to determine if Sildenafil is safe for you. Inform your doctor if you have or have had any of the following conditions:

• Heart problems such as chest pain (angina), heart rhythm disorders, or a heart attack.
• Blood pressure issues, whether high or low.
• Circulatory problems or conditions affecting your blood vessels.
• Eye conditions like retinitis pigmentosa or a history of sudden vision loss.
• Bleeding disorders such as hemophilia.
• Stomach ulcers.
• Liver or kidney disease.
• Pulmonary veno-occlusive disease (PVOD).
• Blood cell disorders such as sickle cell anemia, multiple myeloma, or leukemia.
• Physical deformities of the penis, like Peyronie’s disease.
• Any condition that would make sexual activity unsafe for you.

Age Considerations: Sildenafil (Viagra) is not recommended for use in individuals under 18 years of age.

Dosage and Administration

Sildenafil is available in different forms and dosages, and how you take it depends on what condition you are treating.

For Erectile Dysfunction (Viagra)

Oral dosage form (tablets) for adults up to 65 years of age: The initial dose of Viagra is 50 mg, taken as needed, about 30 minutes to 1 hour before sexual activity. However, you can take it up to 4 hours before sexual activity. The dose can be increased to 100 mg or decreased to 25 mg based on efficacy and tolerability. It is important to note that Viagra should not be taken more than once per day.

Oral dosage form (tablets) for adults 65 years of age and older: 25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Your doctor may adjust your dose if needed.

Children: Use is not recommended.

For Pulmonary Arterial Hypertension (Revatio, Liqrev) 

Oral dosage forms (suspension or tablets) for adults: The initial dose is typically taken 3 times a day, about 4 to 6 hours apart, with each dose being 20 mg. Maintenance doses may titrate up to 80 mg orally 3 times a day, if required, based on symptoms and tolerability. It’s important to follow your doctor’s instructions carefully to manage your PAH effectively.

Children 1 year of age and older weighing 45 kilograms (kg) or more: 20 mg 3 times a day. Your doctor may adjust your dose as needed and tolerated. However, the dose is usually not more than 40 mg 3 times a day.

Children 1 year of age and older weighing 20 to 45 kg: 20 mg 3 times a day.

Children 1 year of age and older weighing 20 kg or less: 10 mg 3 times a day.

Children younger than 1 year of age: Use and dose must be determined by your doctor.

Oral Suspension: If you are prescribed the oral suspension form, make sure to shake the bottle well before measuring a dose. Use the dosing syringe provided to ensure accuracy, and do not use a kitchen spoon.

Missed Dose:

• Viagra: Since it’s taken as needed, missing a dose is unlikely.
• Revatio: If you miss a dose, take it as soon as you remember. However, if it’s almost time for your next dose, skip the missed dose. Do not take two doses at the same time.

Overdose: In the event of an overdose, seek emergency medical attention or contact the Poison Help Line at  1-800-222-1222. Symptoms of an overdose may include severe dizziness, fainting, or a painful/prolonged erection.  Information is also available online at https://www.poisonhelp.org/help. If the victim has collapsed, had a seizure, has trouble breathing, or can’t be awakened, immediately call emergency services at:

Helpline Numbers:

• U.S. Helpline: 911 or 1-800-662-HELP, 1-800-487-4889 

• Africa Helpline: 112 01-4931260, 01-4978899 

Storage: Store Sildenafil at room temperature of 20C to 25C (68F to 77F); excursions permitted to 15C to 30C (59F to 86F), away from moisture and heat. Keep it out of the reach of children.

Potential Side Effects

Like any medication, Sildenafil can cause side effects. While many people do not experience significant issues, it’s essential to be aware of both common and severe side effects.

Serious Side Effects: If you experience any of the following, stop taking Sildenafil and seek emergency medical help:

• Heart attack symptoms: chest pain or pressure, pain spreading to your jaw or shoulder, nausea, sweating.
• Vision changes or sudden vision loss.
• Painful or prolonged erection (lasting more than 4 hours).
• Ringing in your ears or sudden hearing loss.
• Irregular heartbeat.
• Swelling in your hands, ankles, or feet.
• Shortness of breath.
• Seizures (convulsions).
• Severe dizziness or feeling like you might pass out.

Common Side Effects: The more common side effects of Sildenafil include:

• Flushing (a warm feeling with redness or tingling).
• Headache or dizziness.
• Heartburn, nausea, or an upset stomach.
• Abnormal vision, such as blurred vision or changes in color vision.
• Runny or stuffy nose; nosebleeds.
• Sleep problems (insomnia).
• Muscle pain or back pain.

Managing Side Effects: If you experience any side effects, it’s important to discuss them with your doctor. They may adjust your dosage or suggest ways to mitigate these effects. It’s also crucial to follow up regularly to ensure that Sildenafil is working as expected without causing significant issues.

Reporting Side Effects: You can report side effects to the FDA at 1-800-FDA-1088. This helps gather more data on the safety and efficacy of the medication.

Drug Interactions

Sildenafil can interact with various medications, potentially leading to serious side effects or reducing the effectiveness of one or both drugs.

Dangerous Interactions:

• Nitrates: As mentioned earlier, do not take Sildenafil with nitrate medications for chest pain or heart problems. The combination can cause a life-threatening drop in blood pressure. Always inform your healthcare provider about any medications you are taking.
• Riociguat (Adempas): Avoid Sildenafil if you are taking this medication for PAH, as the combination could be dangerous. Discuss alternative treatments with your healthcare provider.
• Other ED Medications: Avoid using Sildenafil with similar medications like avanafil (Stendra), tadalafil (Cialis), or vardenafil (Levitra). Taking these together increases the risk of severe side effects and may not provide additional benefits.

Other Medications: Inform your doctor if you are taking any of the following:

• Blood pressure medications or drugs used for prostate disorders are important to consider, as they may interact negatively with Sildenafil. These interactions can lead to increased side effects or reduced effectiveness of the treatment. It is essential for patients to inform their healthcare provider about all medications they are currently taking, including those for blood pressure and prostate issues, to ensure safe use of Sildenafil.
• Antifungal medications such as ketoconazole or itraconazole can also pose risks when taken alongside Sildenafil. These drugs may alter the way Sildenafil is metabolized in the body, potentially leading to increased side effects. Patients should always discuss their complete medication list with their healthcare provider to avoid any harmful interactions.
• HIV/AIDS medications like ritonavir are another category that can interact with Sildenafil. Ritonavir can increase the levels of Sildenafil in the bloodstream, which may heighten the risk of experiencing sildenafil side effects. Therefore, it is crucial for individuals taking these medications to consult their healthcare provider before starting Sildenafil.

This list is not exhaustive, so always check with your doctor or pharmacist before starting or stopping any medication.

Alcohol and Grapefruit: Drinking alcohol or eating grapefruit while taking Sildenafil can increase the chances of experiencing side effects. It’s best to limit alcohol consumption and avoid grapefruit products during your treatment.

Supplements and Herbal Products: Some supplements and herbal products may also interact with Sildenafil. Be sure to discuss any alternative or complementary therapies you are using with your doctor.